/**
  *Tween 缓动相关
  */
 const tween = {
	Linear: function(t, b, c, d) {
	   //t当前时间，b初始值，c变化量，d持续时间
		return c * t / d + b;
	},
	Quad: {
		easeIn: function(t, b, c, d) {
			return c * (t /= d) * t + b;
		},
		easeOut: function(t, b, c, d) {
			return -c * (t /= d) * (t - 2) + b;
		},
		easeInOut: function(t, b, c, d) {
			if ((t /= d / 2) < 1) return c / 2 * t * t + b;
			return -c / 2 * ((--t) * (t - 2) - 1) + b;
		}
	},
	Cubic: {
		easeIn: function(t, b, c, d) {
			return c * (t /= d) * t * t + b;
		},
		easeOut: function(t, b, c, d) {
			return c * ((t = t / d - 1) * t * t + 1) + b;
		},
		easeInOut: function(t, b, c, d) {
			if ((t /= d / 2) < 1) return c / 2 * t * t * t + b;
			return c / 2 * ((t -= 2) * t * t + 2) + b;
		}
	},
	Quart: {
		easeIn: function(t, b, c, d) {
			return c * (t /= d) * t * t * t + b;
		},
		easeOut: function(t, b, c, d) {
			return -c * ((t = t / d - 1) * t * t * t - 1) + b;
		},
		easeInOut: function(t, b, c, d) {
			if ((t /= d / 2) < 1) return c / 2 * t * t * t * t + b;
			return -c / 2 * ((t -= 2) * t * t * t - 2) + b;
		}
	},
	Quint: {
		easeIn: function(t, b, c, d) {
			return c * (t /= d) * t * t * t * t + b;
		},
		easeOut: function(t, b, c, d) {
			return c * ((t = t / d - 1) * t * t * t * t + 1) + b;
		},
		easeInOut: function(t, b, c, d) {
			if ((t /= d / 2) < 1) return c / 2 * t * t * t * t * t + b;
			return c / 2 * ((t -= 2) * t * t * t * t + 2) + b;
		}
	},
	Sine: {
		easeIn: function(t, b, c, d) {
			return -c * Math.cos(t / d * (Math.PI / 2)) + c + b;
		},
		easeOut: function(t, b, c, d) {
			return c * Math.sin(t / d * (Math.PI / 2)) + b;
		},
		easeInOut: function(t, b, c, d) {
			return -c / 2 * (Math.cos(Math.PI * t / d) - 1) + b;
		}
	},
	Expo: {
		easeIn: function(t, b, c, d) {
			return (t == 0) ? b : c * Math.pow(2, 10 * (t / d - 1)) + b;
		},
		easeOut: function(t, b, c, d) {
			return (t == d) ? b + c : c * (-Math.pow(2, -10 * t / d) + 1) + b;
		},
		easeInOut: function(t, b, c, d) {
			if (t == 0) return b;
			if (t == d) return b + c;
			if ((t /= d / 2) < 1) return c / 2 * Math.pow(2, 10 * (t - 1)) + b;
			return c / 2 * (-Math.pow(2, -10 * --t) + 2) + b;
		}
	},
	Circ: {
		easeIn: function(t, b, c, d) {
			return -c * (Math.sqrt(1 - (t /= d) * t) - 1) + b;
		},
		easeOut: function(t, b, c, d) {
			return c * Math.sqrt(1 - (t = t / d - 1) * t) + b;
		},
		easeInOut: function(t, b, c, d) {
			if ((t /= d / 2) < 1) return -c / 2 * (Math.sqrt(1 - t * t) - 1) + b;
			return c / 2 * (Math.sqrt(1 - (t -= 2) * t) + 1) + b;
		}
	},
	Elastic: {
		easeIn: function(t, b, c, d, a, p) {
			if (t == 0) return b;
			if ((t /= d) == 1) return b + c;
			if (!p) p = d * .3;
			if (!a || a < Math.abs(c)) {
				a = c;
				var s = p / 4;
			} else var s = p / (2 * Math.PI) * Math.asin(c / a);
			return -(a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
		},
		easeOut: function(t, b, c, d, a, p) {
			if (t == 0) return b;
			if ((t /= d) == 1) return b + c;
			if (!p) p = d * .3;
			if (!a || a < Math.abs(c)) {
				a = c;
				var s = p / 4;
			} else var s = p / (2 * Math.PI) * Math.asin(c / a);
			return (a * Math.pow(2, -10 * t) * Math.sin((t * d - s) * (2 * Math.PI) / p) + c + b);
		},
		easeInOut: function(t, b, c, d, a, p) {
			if (t == 0) return b;
			if ((t /= d / 2) == 2) return b + c;
			if (!p) p = d * (.3 * 1.5);
			if (!a || a < Math.abs(c)) {
				a = c;
				var s = p / 4;
			} else var s = p / (2 * Math.PI) * Math.asin(c / a);
			if (t < 1) return -.5 * (a * Math.pow(2, 10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p)) + b;
			return a * Math.pow(2, -10 * (t -= 1)) * Math.sin((t * d - s) * (2 * Math.PI) / p) * .5 + c + b;
		}
	},
	Back: {
		easeIn: function(t, b, c, d, s) {
			if (s == undefined) s = 1.70158;
			return c * (t /= d) * t * ((s + 1) * t - s) + b;
		},
		easeOut: function(t, b, c, d, s) {
			if (s == undefined) s = 1.70158;
			return c * ((t = t / d - 1) * t * ((s + 1) * t + s) + 1) + b;
		},
		easeInOut: function(t, b, c, d, s) {
			if (s == undefined) s = 1.70158;
			if ((t /= d / 2) < 1) return c / 2 * (t * t * (((s *= (1.525)) + 1) * t - s)) + b;
			return c / 2 * ((t -= 2) * t * (((s *= (1.525)) + 1) * t + s) + 2) + b;
		}
	}
};


module.exports = tween


// Linear：线性匀速运动效果；
// Quadratic：二次方的缓动（t^2）；
// Cubic：三次方的缓动（t^3）；
// Quartic：四次方的缓动（t^4）；
// Quintic：五次方的缓动（t^5）；
// Sinusoidal：正弦曲线的缓动（sin(t)）；
// Exponential：指数曲线的缓动（2^t）；
// Circular：圆形曲线的缓动（sqrt(1-t^2)）；
// Elastic：指数衰减的正弦曲线缓动；
// Back：超过范围的三次方缓动（(s+1)*t^3 – s*t^2）；
// Bounce：指数衰减的反弹缓动。
// 每个效果都分三个缓动方式，分别是：

// easeIn：从0开始加速的缓动，也就是先慢后快；
// easeOut：减速到0的缓动，也就是先快后慢；
// easeInOut：前半段从0开始加速，后半段减速到0的缓动。